Personally, this one is the best painkiller I've played. I really enjoyed the new, bigger maps with lots of enemies to defeat, and with a huge variety of ways you can use to engage the enemy. Storyline is also good and well defined, with cool comic-like cutscenes that pretty much explain everything you're doing.
On the other hand, enemy AI isn't great, and they always try to mass attack you and eventually they always gets stupidly stuck somewhere before reaching you. Also there are some medium bugs that can prevent you from going foward on the map, but you can get over them if frustration doesn't beat you first.
Anyway if the part you enjoy the most about FPS games is the amount of enemies to kill and you like them with a little taste of horror, this one won't disapoint you for sure. It's a 6/10 for me.